How can I do this without GATs?

[andresovela]

Hi y'all,

I want to implement IntoIterator for a struct Rgb666(u8, u8, u8), so that it basically returns those 3 u8's in an iterator form.

How can I do it? I attempted this and failed because it requires Generic Associated Types which are unstable:

impl<'a> IntoIterator for Rgb666 {
    type Item = u8;
    type IntoIter<'a> = Iter<'a, Self::Item>;

    fn into_iter(self) -> Self::IntoIter {
        [self.0, self.1, self.2].into_iter()
    }
}

What else can I do to achieve that?

[cole-miller]

pub struct IntoIter(std::array::IntoIter<u8, 3>);

impl Iterator for IntoIter {
    type Item = u8;
    
    fn next(&mut self) -> Option<Self::Item> {
        self.0.next()
    }
}

pub struct Rgb666(u8, u8, u8);

impl IntoIterator for Rgb666 {
    type Item = u8;
    type IntoIter = IntoIter;
    
    fn into_iter(self) -> Self::IntoIter {
        let Self(r, g, b) = self;
        IntoIter(std::array::IntoIter::new([r, g, b]))
        // or `IntoIter([r, g, b].into_iter())` in edition 2021
    }
}

The point of IntoIterator is that creating the iterator consumes self (hence "into"), so your IntoIter type can't borrow from self.